The present invention relates, in general, to a switching device.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Switching devices of a type involved here disconnect a line network from the power grid in the event of excess currents in the line network lasting for a presettable time, in order to prevent further supply of electric current. This prevents damage, for example a cable fire that could occur due to increased heat-up of the conductor from the excess current flow. Such switching devices therefore have a so-called overcurrent trigger device which may include a bimetallic element that is heated by the current flowing in the line network, causing the bimetallic element to bend. At a presettable degree of bending of the bimetallic element which is proportional to a presettable heating of the line network, the bimetallic element triggers a mechanical trigger device which disconnects the switching contacts of the switching device and prevents further current flow.
Conventional switching devices are very inaccurate in triggering the switching device so that the reproducibility for triggering the switching device is very poor, in particular when the overcurrent is small. The switching device is often triggered too late—in particular for a small overcurrent where the switching device should be triggered after a longer time—which may cause problems. This exposes people and systems to risks.
It would therefore be desirable and advantageous to provide an improved switching device to obviate prior art shortcomings and to enhance accuracy, degree of reproducibility for triggering the switching device and adjustment of the overcurrent trigger device.